Uh, considering they're almost 50 yrs old you may want to consider buying something newer ...
Large Advents (1974) woofer pops with deep bass.
I have taken the woofer out of cabinet and swapped it to the other speaker to se if it might be a problem with capacitor but it still did the same in other cabinet. Seems to Pop on deep bass when cone is traveling out. Can I repair this or should I replace the woofer?